EUV lithography is a next-generation lithography technology that uses an exposure wavelength of 13.5 nm. The exposure principle of EUV lithography is analogous to that of conventional lithography in that a mask pattern is transferred with an optical projection system. However, a refractive optical system cannot be used because there is no material which is light-transmitting in the EUV light energy region. Therefore, a reflective optical system must be used, and all the optical elements including the photomask need to be reflective. To enable reflection at 13.5 nm, a series of alternative Mo/Si bilayers are deposited on square mask substrates which are commonly 6.35 mm thick. The substrates need to have an ultra-low thermal expansion coefficient, and they require sub-Angstrom surface roughness, sub-50 nm P-V flatness, and as close as possible to zero defects that are larger than 1 nm in height/depth. Current techniques for CMP using abrasive particles produce mask substrates with too many random sub-10 nm pit-type defects and scratches. Moreover, cleaning the substrates after CMP to remove abrasive particles adds to the pit count and enlarges the scratches.